1) Enhance the image using any options in Image>Adjustments Menu.
a) Levels
b) Curves
c) Color Balance
d) Shadow/Highlight
2) Once specific areas are optimized to obtain desired results, go to the History palette and create a New Snapshot. Name Snapshot accordingly (eg. Sky).
* After Snapshots are created, undo History states until the changes are removed.
3) Next, select the History Brush from the tool palette and choose the proper History Snapshot to paint from as the source. Paint with History on the layer.
* Painting with History is a great way to gradually improve tones and color.
4) Continue as needed, create multiple Snapshots to paint from using the History Brush. It is also possible to select areas and Edit>Fill using History.
* Use common selection tools such as the Magic Wand and Lasso.
5) Painting with History became popular when Photoshop had no layering capabilities. It is still another great way to demonstrate selective control.
* History states and Snapshots are only available for the current session. Once the document is closed, the History and its Snapshots are removed.